high frequency intermittent noise

@erik_squires I unplugged my AV system completely, cable modem included.  It was all off and unplugged.  No affect.  Thanks for the pointer to Furman, I'll check them out.

Doing research, I came across this guy demonstrating a switching power supply noise in the studio:

https://www.youtube.com/watch?v=yremMhceSyI&t=111s

His noise he demonstrated sounds similar to what I am experiencing. If this is the case then @erik_squires may have the right idea with a Furman.

I may have two noise issues in my recording in the original post - 

1. An intermittent high frequency noise
   
2. A consistent high frequency noise like a switching power supply
   

@yogiboy The only fix for the cell tower would be a faraday cage?  I have researched EMF curtains to put up behind my system.

Actually the new hot spot is Hudson Yards, that is where new construction is happening.  But I hear you, our infrastructure is falling apart.

@georgehifi He wanted to have the best possible sound off the grid, so he went with a battery power supply.

@erik_squires Good idea, I just did what you suggested, but it did not work.  I even turned off all but the mono blocks, so it was just the left channel and right channel amps on, nothing else in the household.  The intermittent noise appeared.

@randy-11 The cell tower..next time I see them working on the tower, I’ll wave them down...hey can ya turn it off for a few?

Another circuit, yes I’ve tried that as well. Good idea though. I wish I knew how to use an oscilloscope and had one handy. This was very interesting:

https://www.youtube.com/watch?v=BFLZm4LbzQU

I would like to measure the Furman product with an oscilloscope to see the difference.  Has anyone tried to measure Common Mode Noise from a Furman?

@erik_squires The Furman looks promising.  The P 2400 IT looks like the way to go.

@almarg I checked 540kHz and for a moment, I thought I was in that movie Contact, I did not hear the noise.  Just static.  Great idea.

@falconquest Thank you for the pointer, I will check that out.

I live in a neighborhood where we have the oldest electrical system in the city.  A few years back, an underground power transformer blew up and caused quite a stir in the neighborhood - black smoke from the electrical fire coming out of a manhole from the street. 🔥 

Nothing gets replaced unless it fails, so it would seem for my neighborhood.  I don't think the electrical company would even give me any time considering the issues they are dealing with. 😊

@jea48 The noise does present itself 24 hours a day randomly, it is only the early mornings ~ 4am to 11am it is not very frequent, but it does appear.  The building is 15 stories high.  I have already had 2 different electricians in, and they did not do anything.

As I was writing my last post I realized another important fact:

• The subway runs under my building.
  

I just noticed the noise appearing when I listened for a train to go by.  There seems to be a correlation here, perhaps it's the subway system:  when I hear the subway go by, the noise is apparent.  That would also make sense in that the subway does not run as frequent in the early hours of the day.

@willemj Very good distinction.  I think the battery powered radio was a test to see if it was air born, which leads me to think it is not.  So then it is in the power.  I hope this is the case.  I have a Furman P-2400 IT on order, I'm going to give this a try.  @falconquest and @erik_squires are pointing in this direction, and I have not tried this solution yet.  I will report back my findings on the Furman.

If I listen carefully, I can hear the train go by underneath my building,  There is a low frequency buildup when this occurs looking at a real time analyzer, and I can actually hear the subway cars on the rails, so today I am listening carefully in between records to see if there is a correlation.

This issue is a low level issue, the noise I hear is just beneath the noise floor of the room.  So I'm chasing out the-last-bit of noise in my system. It's always that last 5% that is difficult. 🤓

@jea48 Funny you should mention socket outlets, I just changed my socket outlet from a generic to a Furutech outlet (audiophile brand).  When I opened up the original socket, there were only 2 connections made with no ground.  That is how I know there is no ground.  I looked in the socket for a ground wire and did not find one, so when I swapped out the outlets, I simply mirrored the previous installation - no ground wire to connect.

@jea48 Thank you for all your expertise.  I will pick up that receptacle tester and check it out.

@toddverrone  

I agree, I've listened to people on YouTube playing the sound of cell towers through their test tools, and it sounds like cell tower noise to me as well.

What if the cell phone tower across the street is injecting noise into the electrical system?  Perhaps they have an installation issue?  The cell phone tower was installed about 2 years after I moved in.  But back then, I did not have high resolution system, and was not listening as critically as I am now.

@jea48

This noise issue has been in my system for as long as I have used my system in my current apartment. So it was there before I swapped out my receptacle outlet.  Keep in mind, this noise is just below the noise floor of my apartment, so you have to focus to hear it.  Once you recognize the noise, then it becomes apparent in listening.  I have been on a hunt to chase out all the noise in my system, and this is the last bit of noise that I am aware of.  I can record the noise like I did above with the microphone up to the speaker.  I can see the noise in the real time analyzer as a peak around 6kHz.

I have the plug-in circuit checker on order and it will arrive tomorrow. I also have another receptacle outlet on order as well, as I will be changing the outlet receptacle from a 15 amp to 20 amp outlet receptacle. This is so I can plug the Furman P-2400 IT into the wall. I will be receiving that unit tomorrow as well, so big day for my system tomorrow. There is a possibility I will have my noise issue resolved. I will report back ASAP. 👍🏻

@kosst_amojan  

My interconnects are all shielded, but they could be under-shielded.  If I turn everything off in my system except for my amps, I can still hear the noise.  So in that case we would look at the speaker cables, they are shielded too.  When I turn on my pro-audio monitors plugged into the same circuit or a different circuit, they exhibit the noise too (that rules out my system).  Keep in mind, these pro-audio monitors are self powered with class AB amps built into the speaker enclosure, so it's a self contained amp/speaker.

I do not have the noise on my TV or computer.

I did think about the tubes picking up the noise because on my amps, all the tubes are out in the open?  But then I had a solid state phono preamp in my system just recently, and that picked up the noise as well, so that rules out the tube theory.

It's 15.

Seems like I have been in similar odds before.  Just this weekend I ordered some parts for my turntable from KAB USA, another person with the identical name was ordering parts as well and our orders got combined which turned into an administration mess for Kevin at KAB.  What are the odds?

@jea48

Yes, this is a dedicated circuit, I have tested for this.

When I changed out the outlet, there were 2 wires connected to the old receptacle: white and red. There is another black wire not being used. I didn’t want to touch that wire, since I don’t really know what I am doing, I just copied the previous installation, using only the red and white wires previously used. The insulation seems to be fair, it’s PVC/plastic and the white looks white and did not appear brittle.

I would say the insulation is in good condition.

I will have someone come in and take a look at the circuit, maybe it can be switched out for a 20 amp circuit. So far though, I’ve never tripped the circuit breaker, and my amps are class A.  Thank you for the kind words.

@kosst_amojan

Faraday cage is the next logical step, if the power is clean and the Furman has no affect on the noise.  I've found some copper mesh curtains I can put up behind my system, which would create a barrier.

I'm not aware of any picocells or femtocells in the building.  With a cell tower right across the street, I get good reception in my apartment/building, so no need for devices like those.  All though, I cannot be certain about my neighbors, anything is possible. 

It's 4:45 and rush hour is upon us, I can hear the trains below, and the noise through my system. 👍🏻

I didn't think so, but that is as far as my research went.  Glad I stopped there.

Would the same logic apply if the pro-audio monitors have a balanced input?  No RCA inputs, just XLR.

@jea48 

I had the monitors connected to my preamp through a set of XLR interconnects.

I just went looking for my pro-audio monitors and just realized they are downstairs in storage.  I will dig them out if the Furman P-2400 IT has no affect.  I will be receiving the unit today.

If this noise is coming from the cell tower, I don't think there will be much I can do about it.

@randy-11

My Interconnects are single-ended RCA only.  I cannot switch to balanced because my system does not support it.  I can run balanced from my preamp to amps, but I do not have any XLR interconnects that long.

@jea48

I plugged in the socket tester and got two double orange lights indicating CORRECT. So I do have a ground?

@toddverrone  

Make me go and dig up the instructions..🤓  CORRECT is good all the way around, so I do have a ground.

RCA interconnects range from 3 meters to 1 meter.  Speaker cables are 2.5 meters.

The Furman P-2400 IT has no affect on the noise.

@jea48 

I do not have a radio that is AC powered.  I will look into the RCA shorting plugs.

I think this is an air borne issue - cell tower...

I put the PS Audio Noise Harvesters on the Furman P-2400 IT to see if they would stop blinking, they did not.  And when I turned on my light on a dimmer in the kitchen (different circuit), the PSNHs went crazy.  So does the Furman even do anything to filter noise?

The noise floor in the music has been lowered.  There is benefit sonically in the music though.

@jea48   

No headphone output on my preamp.  

I just dug out my pro-audio monitor too, plugged it into a different circuit and could hear the noise, though not as loud, and nothing was plugged into the monitor either, it was simply plugged into the wall.

@toddverrone

That’s a great find. Let’s say I get ferrite beads in place. I still have tubes out in the open where the audio signal goes through as well. I think there is no escape...

Here is another recording taken early in the morning with no subway cars under my building:

https://clyp.it/ae0xgczb

Note there are 2 noises:

1. The consistent hash/whine
   
2. The intermittent noise
   

This is the worst I've heard it in the mornings.  It only lasted for a minute and a half, enough for me to record the 1 minute clip.

The Furman has buffered me from my refrigerator noise, I would hear a *click* in my system when the refrigerator would turn on, now it's silent.

@whart 

There is now cell phone reception in the subways too.  So each subway car or perhaps the subway tunnels are lined with these devices.

The subway goes right under my building.

No, my phone has no affect.  I wonder if it's because I'm on Verizon, and the offending tower may be a GSM tower?

@jea48   

LOL, Yes, I know where my cell phone is.  I tried turning it off, no effect.

My system does sit against the outside wall, which is at the same level as the cell phone tower.  I do not directly face the tower, but the tower is in direct line of sight just 2 units to my right, so for line of sight purposes, it may as well be right in front of my unit.  I also have the Empire State Building in direct line of sight, and a friend of mine thinks the Empire State Building is radiating all kinds of emissions...says I need to be wearing sunscreen while listening to my system because of the Empire State Building.

I will post a photo on my system page so you can see the towers.

The problem with the towers is they are nondescript - no signs indicating ownership or contact info.  All I see on the towers are WARNING labels everywhere.
That is an outstanding post you found on ProSoundWeb.  Thank you very much with all of your attention on this thread.  You are a real asset to the community.

Thank you EVERYONE who has participated on this thread for that matter.  I really do appreciate your ideas and posts.

I thought it was my interconnects.  I turned off everything except my amps, then I disconnected the interconnects, the noise disappears for a while...but reappeared.  Maybe my speaker cables are suspect too...

Something I’ve been looking at to correlate the noise to the cell tower:

https://www.amazon.com/gp/product/B007L09DLY/ref=s9u_simh_gw_i2?ie=UTF8&fpl=fresh&pd_rd_i=B007L09DLY&pd_rd_r=68bbfce7-caf8-11e7-8cdf-51a46fae6b0a&pd_rd_w=4szrl&pd_rd_wg=JjucN&pf_rd_m=ATVPDKIKX0DER&pf_rd_s=&pf_rd_r=T88X159BY8J205PDCWS2&pf_rd_t=36701&pf_rd_p=8f696f0a-3abd-4660-b9bd-1931764e0008&pf_rd_i=desktop

Here is an example of cell phone noise:

https://www.youtube.com/watch?v=s99i0H-nBw4

If I had the tool, I would be able to correlate with certainty.

I have asked if stopping resistors are used, waiting to hear back.

I found a set of RCA shorting plugs. I turned everything off except for one mono block, inserted the RCA shorting plug, and the noise is still present.

I tried a different power cord, and the noise is still present.

I tried an XLR cable between my power amp and preamp, the noise is still present.

I have ferrite beads (made of material 61) on order.

The power cord is my antenna, I switched to a non-audiophile power cord and was able to move the power cord around, up, down, and around (could never do that with what I am using), and yes, I could affect the noise.

I'm wondering if I'm now in the market for a new power cord?

I don't, I will go and get some...

I just got off the phone with Rob at Furman. He’s a great guy, been in the pro-audio business for 24 years, 16 at Furman. He says he’s seen music studio’s go through the same issue, all of a sudden an antenna gets put up and there’s nothing to do except move. I cannot move, so then he said the next approach is to build a faraday cage and opt for better shielded cables.

This is an air borne issue, the cell tower is coupled to the air, Rob was amazed. I sent him the 2 sound samples I posted here so he could hear.